This invention relates generally to an furnace and associated heat exchanger that are arranged in a generally linear configuration and, more particularly, to a heat exchanger that can be positioned behind the furnace to extract heat therefrom for dispersion into the surrounding environment or to a remote location.
Generally, multi-oil furnaces, sometimes referred to as a used-oil fired furnace because of the primary utilization thereof to burn used oil removed from automobiles and the like as well as standard grades of fuel oils, utilize an air-to-air heat exchanger with a blower than moves ambient air through the furnace structure and/or around the combustion chamber to transfer heat generated within the combustion chamber to a remote location for desired utilization thereof. An efficient air-to-air heat exchanger is shown and described for multi-oil furnaces in U.S. Pat. No. 5,494,025, issued to Benjamin K. Smoker and David J. Yoder on Feb. 27, 1996. This heat exchanger generally surrounds the burner chamber by circulating the combustion gases from the rear of the furnace by an upper set of conduits leading to a header in front of the furnace and then through a lower set of conduits to the rear of the furnace again where the gases are exhausted from the furnace. The ambient ventilation air is passed vertically through the assembly to absorb heat from the conduits and the burner chamber before being discharged from the furnace.
The heat exchanger described in U.S. Pat. No. 5,494,025 requires a cabinet shell having a height greater than the height of the burner chamber due to the upper and lower banks of conduits transferring the combustion gases around the burner chamber to exchange heat with the ambient ventilation air. Likewise, the width of the cabinet shell is required to be greater than the width of the burner chamber. In some installations, the height and/or width requirements will not permit the utilization of a cabinet shell that is significantly greater than the corresponding dimensions of the burner chamber.
Accordingly, it would be desirable to provide a multi-oil furnace that orients the air-to-air heat exchanger substantially rearwardly of the burner chamber so as to minimize the height and/or width dimensions of the furnace cabinet shell.
The thermostat controls for the switch associated with the operation of the fan is conventionally mounted on the circular combustion chamber to sense the temperature of the burner chamber. The switch is operable to start the motion of the fan to push room air through the heat exchanger when the combustion chamber has obtained a high enough temperature to expel warm air through the heat exchanger. Other thermostatic switches control the operation of the burner and are conventionally mounted in close proximity to the fan switch, but are operable to sense the temperature within the cabinet shell of the furnace. These other thermostatic switches are operable to shut down the burner in the event the temperatures get too high, such as could result if there is a failure in the fan to blow the cooling room air through he heat exchanger, and to control the ability to re-start the burner only when the temperature has sufficiently cooled.
The mounting of a flat fan control switch device on the outer circumference of a circular chamber results in a linear contact between the switch and the burner chamber. Tolerances to establish a properly operable switch in such circumstances are difficult to maintain. Since the fan switch will not start the operation of the fan until a minimum temperature setting has occurred, a fan control switch device that falls outside the acceptable tolerances can result in a premature shut down of the burner, because the temperature in the cabinet shell has increased above the maximum permissible by the other thermostatic switches without causing activation of the fan due to the improper sensing of the temperature of the combustion chamber.
Accordingly, an improved mounting for the fan control switch would be desirable to improve the operational performance of the furnace.
It is an object of this invent ion to provide a heat exchanger for a multi-oil furnace that overcomes the aforementioned disadvantages of the known heat exchangers.
It is another object of this invention to provide a heat exchanger for a multi-oil fired furnace that does not require a large cabinet shell to encase the heat exchanger and combustion chamber of the furnace.
It is still another object of this invention to provide a multi-oil furnace with a heat exchanger that enables the combustion chamber of the furnace to have a diameter and length to avoid impingement, metal deterioration, and carbonization from the operation thereof.
It is a feature of this invention that the heat exchanger does not restrict the diameter of the combustion chamber of a multi-oil furnace with respect to the overall size of the cabinet shell that encompasses the furnace and heat exchanger.
It is an advantage of this invention that the heat exchanger configuration extends the operative life of the combustion chamber because of the lack of restriction on the diameter of the combustion chamber.
It is another feature of this invention that the heat exchanger is formed with a plurality of exhaust tubes positioned behind the combustion chamber to transfer heat from the exhausted combustion gases to room air being circulated through the cabinet shell.
It is another advantage of this invention that the positioning of exhaust tubes in line with the combustion chamber reduces the height and width of the cabinet shell needed to house the heat exchanger for a multi-oil furnace.
It is still another feature of this invention that the exhaust tubes are connected to an exhaust header to collect the exhausted combustion gases before being discharged from the furnace.
It is still another advantage of this invention that the provision of an exhaust header rearwardly of the combustion chamber enables the combustion gases to be discharged from either side of the furnace.
It is still another feature of this invention that the exhaust header is provided with multiple discharge outlets for selective use to discharge the combustion gases from the furnace.
It is still another object of this invention to enhance the exchange of heat from the combustion chamber to room air being circulated through the cabinet shell.
It is yet another feature of this invention that the combustion chamber is provided with horizontal baffles to direct room air into a generally laminar flow over the surface of the combustion chamber.
It is still another feature of this invention that the room air is forced through a vertical baffle opening concentric with the combustion chamber before being engaged by the horizontal baffles directing room air along the surface of the combustion chamber.
It is yet another object of this invention to control the flow path of the room air through the cabinet shell in a manner to maximize the transfer of heat from the combustion process to the room air.
It is a further feature of this invention that room air is directed through a central opening through the exhaust header to cause room air to be circulated between exhaust tubes extending between the combustion chamber and the exhaust header, before being forced through an annular opening in a vertical baffle around the combustion chamber and into engagement with horizontal baffles to direct the room air into a laminar flow pattern along the surface of the combustion chamber.
It is a further advantage of this invention that the heat exchanger configuration causes room air to be circulated more equally to prolong the life of the heat exchanger due to stresses resulting from unequal heat distribution.
It is a further object of this invention to provide an improved mounting of the fan control switch on the combustion chamber to enhance the sensing of the temperature of the combustion chamber.
It is yet another advantage of this invention that the control of the operation of the blower fan to move room air through the heat exchanger is improved.
It is still a further feature of this invention that the fan control switch is mounted on a linear plate welded to the top of the combustion chamber for a consistent planar contact between the fan control switch and the combustion chamber.
It is a further advantage of this invention that the sensing of the temperature of the combustion chamber is sensed more accurately for the controlling of the operation of the blower fan on a multi-oil fired furnace.
It is still a further advantage that the contact between the fan control switch and the combustion chamber is planar, rather than linear, due to the welding of a mounting plate on the combustion chamber and forming an integral part thereof.
It is yet a further object of this invention to provide a heat exchanger for use with a multi-oil furnace which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use.
It is still another object of this invention to provide a mounting for a fan control switch for use on a multi-oil fired furnace which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use.
These and other objects, features, and advantages are accomplished according to the instant invention by providing a multi-oil fired furnace having a heat exchanger that extends rearwardly of the combustion chamber and utilizes laminar air flow around the combustion chamber to minimize the width and height dimensions of the cabinet shell for the furnace. The heat exchanger includes an exhaust header having a central opening and a cluster of concentrically arranged exhaust tubes connected to the combustion chamber. A vertical baffle forces the flow of air through a central opening that is concentric with the combustion chamber into a group of horizontal baffles directing the air into a generally laminar flow pattern against the outer surface of the combustion chamber before being discharged from the cabinet shell in a selected one or more of three possible directions. The fan control switch is mounted on a mounting plate that is welded to the combustion chamber to provide a planar contact surface for the switch mechanism.